A wide variety of impeller arrangements have been utilized with two-pole or bipolar permanent magnetic motors. In conventional designs, the impellers are designed to rotate in both the clockwise direction and the counter-clockwise direction. This is because of the random nature of rotational startup of the motor. The random startup of such conventional design creates different operational flow rates, depending upon the direction of rotation, and thereby unpredictability in performance and efficiency.
Some impellers have been designed to provide a preset direction of rotation. One such impeller design is disclosed in U.S. Pat. No. 6,488,484. In this design, the blades of the impeller are configured to provide an imbalance of motor power versus fluid power. Thus, these types of impeller design require specific blade geometry to accomplish unidirectional rotation. Specific blade geometries that accomplish uni-directional rotation are often inefficient or have low performance ratings for particular applications. For example, some impellers having specific blade geometry cause a higher power draw on the motor than impellers having a more standard blade configuration. Similarly, impellers having specific blade geometry are significantly limited in permitting blade modifications to optimize performance because of the design constraint to provide the uni-directional rotation. In impeller designs having a specific blade geometry, performance and efficiency are sacrificed for consistency of directional rotation.
In general, improvement has been sought with respect to such impeller designs, generally to: provide unidirectional rotation without sacrificing performance, and permit use of a variety of a high performance impeller blade configurations while still providing a known direction of rotation.